Glaswegian comedian Susan Calman was reduced to tears after being targeted on Twitter for remarks she made on the BBC Radio 4 News Quiz this week.

Abuse has also been hurled at journalists and public figures, while politicians have been trading increasingly nasty insults.

Giving the Judith Hart memorial lecture in Lanarkshire tonight, Paisley and Renfrewshire South MP Alexander will say the time has come for the debate to get out of the gutter.

He will say: “All of us here in Scotland – whatever our party affiliations and whatever our views on the referendum – should condemn unequivocally statements and actions that poison the well of public debate and demand a different and better conversation ahead of Scotland’s choice.

“It seems to me the real debate we need is not who we are, but how we are – not a divisive and bitter battle for standing, but a respectful offering of differing visions for the future of our nation.

“ We need vision, not viciousness, as we make our choice.

“If we are to discuss a new vision for an old nation, then to my mind, it is the essence of that vision and what has to be done together to achieve it that must be to the fore in such discussion.”

Alexander will look to the example of Enlightenment figures like David Hume for an intellectual and rational approach to the debate.

He will add: “With just over a year to go until the referendum, the prospect of independence has not produced a single major theoretical work of note.

“Instead, despite the handsome and historic victory of the SNP in 2011, too often the advocates of independence seem to have satisfied themselves with decrying their opponents.

“This week, we saw the SNP’s Angus Robertson attempt to belittle the campaign against independence by branding people who opposed separation as having the view that ‘people in Scotland are uniquely poor, stupid and incapable of governing themselves’.

“As a supporter of the Better Together campaign, I find this characterisation not just inaccurate, but crass and offensive.

“More importantly, however, it patronises the Scottish people who are quite capable of making an informed choice between different viewpoints without one side denigrating the other.

“Yet what should concern us even more is that systematic denigration of fellow Scots is now directed at even those far beyond party politics.”

The speech represents the second major intervention in the independence debate by Alexander, a key ally of Labour leader Ed Miliband.

He previously called for a national convention to be set up to consider the future of Scotland if independence is rejected. His speech tonight goes on: “I believe that neighbourliness – not walking away – has shaped my sense of who as Scots we are. And that we do not need to walk away to be the Scots we want to be.

“And I believe that a decision to not walk away from our neighbours in 2014 will allow us to together chart a new vision for an old nation.”

A spokesman for the SNP last night agreed that the independence debate had descended into mud-slinging.

He added: “We agree with Douglas Alexander.

“Denigration of people has no place in the referendum debate. It doesn’t matter whether they support Yes or No.

“It’s a matter of public record that Nicola Sturgeon has been sent death threats on Twitter, a posting on the No campaign’s Facebook page talked about firing bullets into SNP leaders, appalling remarks about Alex Salmond’s dad were made on a Labour Party website and the abuse directed at Susan Calman was disgraceful.

“All of it must stop because the referendum debate needs to be a positive one with the people about what Scotland can achieve as an independent country.”